1. FIELD OF THE INVENTION
The present invention relates to a process for repeatedly producing p-chloroalkylbenzene in high selectivity.
2. DESCRIPTION OF THE PRIOR ARTS
The ring chlorinated alkylbenzenes are useful as reagents for various organic syntheses for producing medicines and agricultural chemicals etc. A demand of p-chloroalkylbenzenes such as p-chlorotoluene is large.
In the conventional chlorination of an alkylbenzene with chlorine gas in the presence of a Lewis acid such as antimony chloride, ferric chloride and aluminum chloride, an o-chloroalkylbenzene has been mainly produced and m-chloroalkylbenzene and polychlorinated compounds as by-products have been produced. It has been difficult to obtain a p-chloroalkylbenezene at a high yield such as higher than 40%.
In order to produce p-chloroalkylbenzene at high yield, various catalysts have been developed. For example, a p-chloroalkylbenzene has been produced at an yield of 45 to 52% by using a Lewis acid and sulfur or selenium as a catalyst. A p-chloroalkylbenzene has been produced at an yield of 55 to 60% by using a Lewis acid and thianthrene as the catalyst (Japanese Unexamined Patent Publication 19630/1977). The process using a Lewis acid and thianthrene as the catalyst give remarkably high selectivity to p-chloroalkylbenzene. However, thianthrene is oxidized in the presence of water to be converted through 5,5-dioxythianthrenes to diphenylsulfides. In the repeated use of the catalyst, the catalytic activity is lowered and the alkyl group as a side chain is chlorinated as a side-reaction.
The inventors have studied to develop a catalyst which give high selectivity to a p-chloroalkylbenzene but has not the disadvantages of thianthrene. As a result, the inventors have found that when a Lewis acid and a phenoxthine compound are used as the catalyst, the selectivity to the p-chloroalkylbenzene is high and the phenoxthine compound is only oxidized to 10-oxyphenoxthine in the presence of water and can be repeatedly used without a deterioration of the catalytic activity and a chlorination of the side chain as the alkyl group is not caused.